MOSCOW--A Kremlin-favored candidate declared victory in Sunday's election for mayor of Moscow, although an independent monitoring group questioned whether he received enough votes to avoid a runoff.

Shortly after midnight Sunday, acting Mayor Sergei Sobyanin appeared before a crowd of several thousand supporters gathered in downtown Moscow and said that while the vote was close, he was confident that he had won. The Moscow Election Commission said that, with 42% of the votes counted, Sobyanin was leading his closest rival, the opposition figure Alexei Navalny, by 52.6% to 26.2%.

However, the independent Alliance of Observers, which sent monitors to more than half of the polling stations, said results from those 1,900 locations showed Sobyanin with only 49.8%. If he fell short of 50%, the race will be thrown into a runoff in two weeks between the top two vote-getters.

A staunch loyalist of President Vladimir Putin, the 55-year-old Sobyanin was appointed mayor in 2010 by then-President Dmitry Medvedev and was running Sunday in his first bid to win a full term in office.

The race drew international attention because Sobyanin's main challenger was Navalny, a popular blogger and anti-corruption crusader who is considered Putin’s most vocal critic. Navalny ran despite his conviction earlier this summer on embezzlement charges, for which he was sentenced to five years in prison. His followers considered the case to be politically motivated.

Most exit polls showed Sobyanin leading with about 53% of the vote, trailed by Navalny at about 32%.

Navalny, 37, insisted that his own exit polls showed Sobyanin falling short of the 50% mark. He warned that the election could be determined by "falsifications."